The present invention is related to a semiconductor process, and especially to a process for manufacturing a trench capacitor having a hill structure.
In the semiconductor process of dynamic random access memory (DRAM), many capacitors are required to construct memory cells for storing the digital data by way of electrical charges. It is an important topic to effectively manufacture more capacitors into a memory IC having a fixed size. There are many structure in the capacitor manufacture. Here the trench capacitor will be mentioned.
Please refer to FIG. 1(a) and FIG. 1(b) showing two DRAM memory cells respectively using the trench capacitor C1 and C2. Each capacitor have a first plate 11, an insulation layer 12 and a polysilicon layer 13. However, its capacitance is constrained by the effective area on sidewall of the trench thereby obstructing the density improvement of DRAM.
Please refer to FIG. 2 showing a trench capacitor having a hill structure without the defect of the capacitor shown in FIG. 1. This trench capacitor has a hill structure 21 formed in the trench for increasing the effective plate area of the trench capacitor. FIG. 3(a) to FIG. 3(c) shows the detailed process flow of fabricating this trench capacitor.
Please refer to FIG. 3(a) showing that an oxide layer 32 is formed on the side-wall of the trench 31 formed on a semiconductor substrate 30 and a surface 301 is exposed after an etching back process.
Please refer to FIG. 3(b) showing that a substrate contact 33 lower than the oxide layer 32 is formed by etching the exposed surface 301 into the semiconductor substrate 30.
As shown in FIG. 3(c), a poysilicon layer is deposited between the contact 33 and the oxide layer 32 and then the oxide layer 32 is etched with HF for forming the hill structure 21. Finally, the trench capacitor having the hill structure in FIG. 2 is fabricated after forming a plate and an insulation layer on the hill structure 21.
However, the above-mentioned conventional process has the following defects:
(1) a contact etching is required for connecting the hill structure of the capacitor with the semiconductor substrate, so the process is complicated.
(2) the contact is positioned in a depth, so the etching process is difficult to implement.
(3) the capacitor has a defect in electricity because the hill structure will results in a contact resistance between the contact and the first plate.
An object of the present invention is to provide an easier process for manufacturing the capacitor having a hill structure.
Another object of the present invention is to reduce the manufacture process and to lower the manufacturing cost.
According to the present invention, the process of manufacturing a trench capacitor having a hill structure includes the steps of providing a semiconductor substrate, forming a passivation layer on the semiconductor substrate, etching the passivation layer to form a trench defined by a side wall and a bottom surface, forming a spacer on the side-wall, wherein the bottom surface includes a first part covered by the spacer and a second part exposed from the spacer, forming a sacrificial layer between the spacer and the second part, and removing the sacrificial layer until the spacer has been fully removed to expose the first part wherein an etched rate of the sacrificial layer is slower than that of the spacer, thereby forming the trench capacitor with the hill structure.
In according with one aspect of the present invention, the semiconductor substrate is made of silicon.
In according with one aspect of the present invention, the passivation layer includes a pad oxide layer, a pad silicon nitride layer, a borosilicate glass (BSG), and a silicon oxynitride layer.
In according with one aspect of the present invention, the trench is formed by photolithography and an etching process.
In according with one aspect of the present invention, the spacer is made of polysilicon.
In according with one aspect of the present invention, the sacrificial layer is made of BSG.
In according with one aspect of the present invention, the hill structure is surrounded by a valley formed in the first part of the semiconductor substrate for increasing an effective area of the trench capacitor having the hill structure.
In according with one aspect of the present invention, surfaces of the hill structure and the valley are doped with a conductive material for forming a first plate of the trench capacitor having the hill structure.
In according with one aspect of the present invention, an insulation layer is formed on the hill structure and in the valley for forming an area for storing an electric charge.
In according with one aspect of the present invention, the conductive material is applied on the insulation layer for forming a second plate of the trench capacitor having the hill structure.
According to the present invention, the process of manufacturing a trench capacitor having a hill structure comprising steps of providing a semiconductor substrate having a trench defined by a side wall and a bottom surface, forming a spacer on the side wall, the spacer covering a first part of the bottom surface but exposing a second part of the bottom surface, forming a sacrificial layer on the substrate and the spacer, firstly removing the sacrificial layer, the substrate and the spacer until the second part is exposed, and the semiconductor substrate under the first part is removed for a certain depth, and secondly removing further the semiconductor substrate under the first part and the second part simultaneously for forming the trench capacitor having a hill structure.
In according with one aspect of the present invention, the semiconductor substrate has a passivation layer formed on the trench, and the semiconductor is made of silicon.
In according with one aspect of the present invention, the passivation layer includes a pad oxide layer, a pad silicon nitride layer, a BSG layer, and a silicon oxynitride layer, and the trench is formed by a hotolithography and an etching process.
In according with one aspect of the present invention, before the firstly removing step, the spacer has been fully removed, but the sacrificial layer above the second part still has a certain height.
In according with one aspect of the present invention, the spacer is made of polysilicon.
In according with one aspect of the present invention, the sacrificial layer is made of BSG.
In according with one aspect of the present invention, the hill structure is surrounded by a valley formed in the first part of the semiconductor substrate for increasing an effective area of the trench capacitor having the hill structure.
In according with one aspect of the present invention, surfaces of the hill structure and the valley are doped with a conductive material for forming a first plate of the trench capacitor having the hill structure.
In according with one aspect of the present invention, an insulation layer is formed on the hill structure and in the valley for forming an area for storing an electric charge.
In according with one aspect of the present invention, the conductive material is applied on the insulation layer for forming a second plate of the trench capacitor having the hill structure.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: